The role of the sheath in magnetized plasma fluid turbulence

In the sheath region at the interface between plasmas and solid surfaces, quasi-neutrality and, in the case of magnetized plasmas, drift-ordering are violated. These two assumptions are typically made in plasma fluid models; the presence of a plasma-wall transition region, typical of all bounded systems, hampers therefore their use. This problem can be overcome by introducing a set of boundary conditions (BCs) for fluid models that properly describe the physics of the plasma-wall transition region. While the classical Bohm-Chodura BCs for the ion and electron parallel velocities have been previously derived, no consistent BCs for the other fluid quantities existed up to date. Based on a recent theory [1,2], a complete set of analytical BCs for the density, temperature, potential, vorticity, and parallel ion and electron velocities, has been provided, which is fully consistent with kinetic simulations of the plasma-wall transition region [3]. These BCs have been implemented in a three-dimensional global fluid code, which is used to simulate turbulence in basic plasma physics devices and in the tokamak scrape-offlayer. It has been shown that BCs that faithfully supply the sheath physics to the fluid codes are crucial for the understanding of the equilibrium profiles, plasma recirculation, intrinsic plasma rotation, and blob propagation in basic plasma physics and fusion devices. References [1] J. Loizu, P. Ricci and C. Theiler, Physical Review E 83, 016406 (2011) [2] J. Loizu, J. Dominski, P. Ricci and C. Theiler, Phys. Plasmas 19, 083507 (2012) [3] J. Loizu, P. Ricci, F. Halpern and S. Jolliet, Phys. Plasmas 19, 122307, (2012)